Download & install the Metamask Wallet either from the app store on your phone or the browser extension for desktop.
Get BNB from your favorite DEX or CEX platform. Remember to leave enough for gas fees.
Head over to Pancake Swap and paste the $ROOST contract address listed on this website to swap your BNB.
Now all you have to do is add the $ROOST contract address to your Metamask Wallet for your $ROOST tokens to show.